U.S. patent number 8,586,644 [Application Number 13/295,132] was granted by the patent office on 2013-11-19 for photocurable composition suitable for rust prevention of a threaded joint for steel pipes.
This patent grant is currently assigned to Chugoku Marine Paints, Ltd., Nippon Steel & Sumitomo Metal Corporation, Vallourec Mannesmann Oil & Gas France. The grantee listed for this patent is Kunio Goto, Ryuichi Imai, Yoshinori Kameda, Takayuki Kamimura, Keishi Matsumoto, Tomomitsu Nagareo, Masaru Takahashi. Invention is credited to Kunio Goto, Ryuichi Imai, Yoshinori Kameda, Takayuki Kamimura, Keishi Matsumoto, Tomomitsu Nagareo, Masaru Takahashi.
United States Patent |
8,586,644 |
Nagareo , et al. |
November 19, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Photocurable composition suitable for rust prevention of a threaded
joint for steel pipes
Abstract
A thin and highly transparent coating having excellent air
tightness, adhesion to a substrate, lubricating properties, galling
resistance, and corrosion resistance is formed on the surface of a
metal substrate and particularly on the surface of a threaded joint
which is used for connection of oil country tubular goods. A
photocurable composition comprising (A) a photocurable
(meth)acrylate resin, (B) a (meth)acrylate monomer selected from a
monofunctional (meth)acrylate monomer and a difunctional
(meth)acrylate monomer, (C) a trifunctional or higher
multifunctional (meth)acrylate monomer, (D) a photopolymerization
initiator, (E) a benzotriazole anticorrosive agent, (F) an
anticorrosive pigment selected from a phosphate anticorrosive
pigment and calcium ion-exchanged silica, and (G) a phosphate ester
is used to form a photocured coating.
Inventors: |
Nagareo; Tomomitsu (Moriyama,
JP), Kameda; Yoshinori (Kusatsu, JP),
Matsumoto; Keishi (Takarazuka, JP), Kamimura;
Takayuki (Takarazuka, JP), Takahashi; Masaru
(Nishinomiya, JP), Goto; Kunio (Kobe, JP),
Imai; Ryuichi (Kainan, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nagareo; Tomomitsu
Kameda; Yoshinori
Matsumoto; Keishi
Kamimura; Takayuki
Takahashi; Masaru
Goto; Kunio
Imai; Ryuichi |
Moriyama
Kusatsu
Takarazuka
Takarazuka
Nishinomiya
Kobe
Kainan |
N/A
N/A
N/A
N/A
N/A
N/A
N/A |
JP
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
Nippon Steel & Sumitomo Metal
Corporation (Tokyo, JP)
Vallourec Mannesmann Oil & Gas France (Aulnoye-Aymeries,
FR)
Chugoku Marine Paints, Ltd. (Hiroshima, FR)
|
Family
ID: |
43297834 |
Appl.
No.: |
13/295,132 |
Filed: |
November 14, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120112456 A1 |
May 10, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2010/059587 |
Jun 1, 2010 |
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Foreign Application Priority Data
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Jun 2, 2009 [JP] |
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2009-132937 |
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Current U.S.
Class: |
522/1; 520/1 |
Current CPC
Class: |
F16L
15/001 (20130101); C09D 175/16 (20130101); C09D
5/086 (20130101); C08F 290/06 (20130101); C08F
290/06 (20130101); C08F 222/1006 (20130101); C08F
290/06 (20130101); C08F 220/12 (20130101); C08F
290/06 (20130101); C08F 230/02 (20130101); Y10T
428/31692 (20150401) |
Current International
Class: |
C08F
2/46 (20060101); C08G 61/04 (20060101) |
Field of
Search: |
;522/1 ;520/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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08-231653 |
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Sep 1996 |
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JP |
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2002-080511 |
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Mar 2002 |
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JP |
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2002-080511 |
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Mar 2003 |
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JP |
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2009-007567 |
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Jan 2009 |
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JP |
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98/36325 |
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Aug 1998 |
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WO |
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2004/063294 |
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Jul 2004 |
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WO |
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WO 2005/059048 |
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Jun 2005 |
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WO |
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2006/075774 |
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Jul 2006 |
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WO |
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2006/104251 |
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Oct 2006 |
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WO |
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2007/042231 |
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Apr 2007 |
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WO |
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Primary Examiner: Choi; Ling
Assistant Examiner: Whiteley; Jessica E
Attorney, Agent or Firm: Clark & Brody
Claims
The invention claimed is:
1. A photocurable composition consisting essentially of: (A) a
photocurable (meth)acrylate resin, (B) a (meth)acrylate monomer
selected from a monofunctional (meth)acrylate monomer and a
difunctional (meth)acrylate monomer, said monofunctional
(meth)acrylate monomer being selected from the group consisting of
2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate,
ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, methyltriglycol (meth)acrylate,
isodecyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl
(meth) acrylate, dicyclopentenyloxyethyl (meth)acrylate, and lauryl
(meth)acrylate, (C) a trifunctional or higher multifunctional
(meth)acrylate monomer, (D) a photopolymerization initiator, (E) a
benzotriazole anticorrosive agent, (F) an anticorrosive pigment
selected from a phosphate anticorrosive pigment and calcium
ion-exchanged silica, and (G) a phosphate ester.
2. A photocurable composition as set forth in claim 1 wherein the
phosphate ester (G) is a (meth)acrylate having a phosphate group in
the molecule.
3. A photocurable composition as set forth in claim 1 wherein the
photocurable (meth)acrylate resin (A) is at least one member
selected from polyester (meth)acrylate, epoxy (meth)acrylate,
polyether (meth)acrylate, and polyurethane (meth)acrylate.
4. A photocurable composition as set forth in claim 1 containing,
in mass parts, 5-50 parts of component (A), 5-50 parts of component
(B), 5-30 parts of component (C), 1-15 parts of component (D),
0.1-5 parts of component (E), 1-10 parts of component (F), and 1-5
parts of component (G), wherein the total of components (A)-(G) is
100 parts by mass.
5. A photocurable composition consisting essentially of: (A) a
photocurable (meth)acrylate resin, (B) a (meth)acrylate monomer
selected from a monofunctional (meth)acrylate monomer and a
difunctional (meth)acrylate monomer, said monofunctional
(meth)acrylate monomer being selected from the group consisting of
2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate,
ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, methyltriglycol (meth)acrylate,
isodecyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl
(meth) acrylate, dicyclopentenyloxyethyl (meth)acrylate, and lauryl
(meth)acrylate, (C) a trifunctional or higher multifunctional
(meth)acrylate monomer, (D) a photopolymerization initiator, (E) a
benzotriazole anticorrosive agent, (F) an anticorrosive pigment
selected from a phosphate anticorrosive pigment and calcium
ion-exchanged silica, (G) a phosphate ester, and further containing
a lubricant.
6. A photocurable composition consisting essentially of: (A) a
photocurable (meth)acrylate resin, (B) a (meth)acrylate monomer
selected from a monofunctional (meth)acrylate monomer and a
difunctional (meth)acrylate monomer, said monofunctional
(meth)acrylate monomer being selected from the group consisting of
2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate,
ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, methyltriglycol (meth)acrylate,
isodecyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl
(meth) acrylate, dicyclopentenyloxyethyl (meth)acrylate, and lauryl
(meth)acrylate, (C) a trifunctional or higher multifunctional
(meth)acrylate monomer, (D) a photopolymerization initiator, (E) a
benzotriazole anticorrosive agent, (F) an anticorrosive pigment
selected from a phosphate anticorrosive pigment and calcium
ion-exchanged silica, (G) a phosphate ester, and further containing
a fluorescent brightening agent.
7. The use of a photocurable composition as set forth in claim 1 as
a material for forming a rust-preventing coating on a threaded
joint for steel pipes.
8. A photocured coating formed from a photocurable composition as
set forth in claim 1.
9. A photocured coating as set forth in claim 8 having a turbidity
of at most 40%.
10. A metal substrate with a photocured coating having a photocured
coating as set forth in claim 8 on the surface of the metal
substrate.
11. A threaded joint for steel pipes with a photocured coating
having a photocured coating as set forth in claim 8 on the surface
of a pin and/or a box of the threaded joint for steel pipes.
12. A rust-preventing method for a threaded joint for steel pipes
including the steps of applying a photocurable composition as set
forth in claim 1 on the surface of a pin and/or a box of a threaded
joint for steel pipes and then irradiating the coated surface with
active energy rays to cure the composition and form a photocured
coating.
13. A method of manufacturing a threaded joint for steel pipes with
a photocured coating including the steps of applying a photocurable
composition as set forth in claim 1 on the surface of a pin and/or
a box of a threaded joint for steel pipes and then irradiating the
coated surface with active energy rays to cure the composition and
form a photocured coating.
Description
TECHNICAL FIELD
This invention relates to a photocurable composition and its use
(such as a photocured coating, a substrate having a photocured
coating, and a threaded joint for steel pipes having a photocured
coating), a rust-preventing method for a threaded joint for steel
pipes using the composition, and a method of manufacturing a
threaded joint for steel pipes having a photocured coating. A
photocurable composition according to the present invention is
particularly suitable for rust-preventing surface treatment of a
threaded joint for steel pipes used for connecting steel pipes, and
particularly oil country tubular goods (OCTG).
BACKGROUND ART
Oil country tubular goods (such as tubing, through which crude oil
or other fluid flow, and casing which surrounds tubing) used for
excavating oil wells for exploitation of crude oil and natural gas
typically have a length of ten some meters and are connected using
a threaded joint until a length reaching an oil well is achieved.
In the past, the depth of oil wells was 2,000-3,000 meters.
However, recently, in deep oil wells such as for undersea oil
fields, the depth of oil wells may reach 8,000-10,000 meters or
more.
In its environment of use, a threaded joint used for connecting oil
country tubular goods is acted upon by loads such tensile forces in
the axial direction caused by the weight of oil country tubular
goods and the threaded joints themselves, compound pressure due to
internal and external surface pressure, and geothermal heat.
Therefore, a threaded joint for steel pipes needs to be able to
maintain the gastightness of oil country tubular goods without
being damaged even in such a severe environment.
A typical threaded joint used for connecting oil country tubular
goods has a pin-box structure such as schematically shown in FIG.
1. A pin 1 is a joint component having a male or external thread 3a
which is typically formed on the end of an oil country tubular good
A. A box 2 is a joint component having a female or internal thread
3b which is typically formed on the inner surface of a threaded
joint member B (a coupling). Unthreaded metal contact portions are
formed close to the distal end of the male thread 3a of the pin 1
and close to the proximal end of the female thread 3b of the box 2.
Gastightness of the oil country tubular good A is guaranteed by
inserting one end of the oil country tubular good A into the
threaded joint member B and tightening the male threads 3a and the
female threads 3b so that the unthreaded metal contact portions of
the pin and the box contact each other.
During the process of lowering tubing or casing into an oil well,
due to various problems, a threaded joint which has previously been
connected is sometimes lifted out of the oil well, retightened, and
then lowered into the well. API (American Petroleum Institute)
requires galling resistance and gastightness such that even if
makeup (tightening) and breakout (loosening) are carried out ten
times for a joint for tubing and three times for a joint for
casing, there is no occurrence of unrepairable seizing referred to
as galling and the gastightness of oil country tubular goods is
maintained.
In order to increase gastightness and galling resistance at the
time of makeup, in the past, a viscous liquid lubricant containing
heavy metal powders (referred to as compound grease) was applied to
the contact surfaces (the threaded portions and the unthreaded
metal contact portions) of a threaded joint. Such a compound grease
is prescribed by API BUL 5A2. Compound grease also exhibits
corrosion resistance (rust-preventing properties) in that it
prevents the formation of rust on the contact surfaces to which it
is applied.
With the object of increasing the retention of compound grease (the
adhesion of grease to the contact surfaces of a threaded joint) and
improving the lubricating properties of a threaded joint, it has
been proposed to perform various types of surface treatment such as
nitriding, plating (such as zinc-based plating or dispersion
plating), or phosphating treatment to form one or more surface
treatment layers on the contact surfaces of a threaded joint.
However, the use of compound grease has the problem that there is a
concern of adverse effects on the environment and humans. Compound
grease contains a large amount of heavy metal powders such as zinc,
lead, and copper. Therefore, at the time of makeup of a threaded
joint, the applied grease is washed off or overflows to the outer
surface, and there is the possibility of harmful heavy metals such
as lead and the like having an adverse effect on the environment
(particularly sea life). In addition, the process of applying
compound grease worsens the work environment, so there is a concern
of toxic effects on the human body.
In recent years, as a result of the enactment in 1998 of the OSPAR
Convention (Oslo-Paris Convention) relating to preventing maritime
pollution in the Northeast Atlantic, strict restrictions with
respect to the environment are advancing on a global scale, and the
use of compound grease is already being restricted in some
regions.
Accordingly, in order to avoid adverse effects on the environment
and humans in the excavation of gas wells and oil wells, a demand
for a threaded joint which can exhibit excellent galling resistance
without using compound grease has developed.
Another problem of compound grease is that it contains a large
amount of a solid lubricant typified by graphite, and it forms a
coating which is not transparent. A pin having a threaded portion
on the outer surface of a tubular body more easily undergoes damage
during transport or at the time of makeup than does a box having a
threaded portion on the inner surface of a tubular body. Therefore,
a pin is often subjected to visual inspection for damage to the
threaded portion thereof prior to makeup operations in order to
avoid the occurrence of sudden galling caused by damage to the
threaded portion of the pin which is formed on the outer surface of
a pipe. When a compound grease has been applied, it was necessary
at the time of inspection to clean the pin by washing the applied
compound grease off and then to reapply compound grease after
inspection. As described above, such operation is harmful to the
environment and is time-consuming. If the coating were transparent,
the threaded portion could be visually inspected for damage without
removing the applied coating, and the labor required for inspection
could be greatly decreased.
After an oil country tubular good is manufactured, it is sometimes
stored for a number of months or longer until it is actually used.
Therefore, "storage grease" is applied to the contact surfaces of a
threaded joint. Like compound grease, storage grease is not
transparent, so each time inspection is carried out, it is
necessary to wash it off. Therefore, like compound grease, storage
grease has an environmental problem.
In below-described Patent Documents 1-3, one of the present
applicants proposed the following threaded joints which can be used
to connect oil country tubular goods without applying compound
grease or storage grease.
Patent Document 1 (WO 2006/104251): A threaded joint in which the
contact surfaces of at least one of a pin and a box are coated with
a coating having a two-layer structure (a two-layer coating) which
is constituted by a lower viscous liquid or semisolid lubricating
coating and an upper dry solid coating. The dry solid coating can
be formed from a thermosetting resin such as an acrylic resin or an
ultraviolet curable resin. Since the viscous liquid or semisolid
lubricating coating is tacky, foreign matter easily adheres to it,
but by forming a dry solid coating atop it, its tackiness is
eliminated. The dry solid coating is destroyed at the time of
makeup of a threaded joint, and this upper coating does not impair
the lubricating properties of the lubricating coating beneath
it.
Patent Document 2 (WO 2007/042231): A threaded joint having a thin,
non-tacky lubricating coating formed on a threaded portion (e.g.,
of a pin or a box). The lubricating coating contains solid
lubricant particles dispersed in a solid matrix exhibiting plastic
or viscoplastic rheological properties (flow properties). The solid
matrix preferably has a melting point in the range of
80-320.degree. C. This lubricating coating is formed by spray
coating in a molten state (hot melt spraying), flame spraying using
a powder, or spray coating of an aqueous emulsion. A composition
used for hot melt spraying comprises polyethylene as a
thermoplastic polymer, wax (such as carnauba wax) and a metal soap
(such as zinc stearate) as a lubricant component, and calcium
sulfonate as a corrosion inhibitor.
Patent Document 3 (WO 2006/075774): A threaded joint in which a
contact surface of at least one of a pin and a box is coated with a
two-layer coating constituted by a lower solid lubricating coating
comprising a lubricant powder and a binder, and an upper solid
anticorrosive coating which does not contain solid particles.
In addition, Patent Document 4 (JP 2002-080511 A1) discloses a
photocurable composition which comprises (A) a photocurable
(meth)acrylate resin, (B) a carboxyl group-containing
monofunctional (meth)acrylate monomer, (C) a (meth)acrylate
phosphate compound, (D) a difunctional (meth)acrylate monomer, (E)
a trifunctional or higher multifunctional (meth)acrylate monomer,
(F) a photopolymerization initiator, and optionally an
anticorrosive pigment. In an example of Patent Document 4, a
composition is illustrated in which a condensed phosphate aluminum
salt is used as an anticorrosive pigment. According to Patent
Document 4, by using the photocurable composition disclosed
therein, a coating having excellent properties in terms of adhesion
to a steel pipe, rust prevention, and surface smoothness can be
formed.
Patent Document 1: WO 2006/104251
Patent Document 2: WO 2007/042231
Patent Document 3: WO 2006/075774
Patent Document 4: JP 2002-080511 A1
SUMMARY OF THE INVENTION
The two-layer coating for a threaded joint described in Patent
Document 1 has excellent lubricating properties and corrosion
resistance. However, it has the problems that (1) it is necessary
to form a two-layer coating comprising a lubricating coating and a
dry solid coating formed atop it, so the coating process is
complicated, (2) at the time of thread makeup, flakes form when the
two-layer coating is destroyed, so the subsequent external
appearance is not so good, and (3) the coating has low
transparency. In addition, there is a desire for a coating having
superior corrosion resistance, adhesion, and other properties.
The coating for a threaded joint described in Patent Document 2
also has superior lubricating properties and corrosion resistance.
However, since this coating is not transparent, it is difficult to
perform inspection in order to check the presence or absence of
damage to the threaded portion.
The coating for a threaded joint described in Patent Document 3 has
extremely high corrosion resistance. However, due to the solid
lubricating coating which is a hard solid coating, even if the
solid corrosion preventing coating formed atop it breaks into
pieces at the time of makeup of a threaded joint, it is difficult
for the pieces to become embedded in the underlying solid
lubricating coating. As a result, the lubricating properties of
this two-layer coating are slightly inferior.
A coating formed from the photocurable composition described in
Patent Document 4 has excellent properties in adhesion to a steel
pipe, rust-preventing properties, and surface smoothness. However,
it has the problems that (1) its adhesion to a substrate is low in
an environment in which high and low temperatures are repeated
which is a typical environment of use of a steel pipe (particularly
an oil country tubular good) such as regions which reach a high
temperature, regions which become extremely cold in winter, and
regions which experience extremes of hot and cold during the day
and night, and (2) although it is thought necessary to have
corrosion resistance which can prevent the formation of rust even
in such environments, the performance of this coating is inadequate
in this respect.
An object of the present invention is to solve the above-described
problems of the prior art. Namely, it is an object of the present
invention to provide a photocurable composition which can form a
coating which has excellent properties in terms of gastightness,
adhesion to a substrate, lubricating properties, galling
resistance, and corrosion resistance without using a compound
grease or a storage grease and which can form a thin film having
high transparency.
Another object of the present invention is to provide a photocured
coating, a substrate with a photocured coating, and a threaded
joint for steel pipes having a photocured coating which are formed
using the photocurable composition, as well as a rust-preventing
method for a threaded joint for steel pipes and a method of
manufacturing a threaded joint for steel pipes having a photocured
coating formed from the photocurable composition.
According to the present invention, the above-described objects can
be achieved by a photocurable composition which comprises the
following components (A) to (G):
(A) a photocurable (meth)acrylate resin,
(B) a (meth)acrylate monomer selected from a monofunctional
(meth)acrylate monomer and a difunctional (meth)acrylate
monomer,
(C) a trifunctional or higher multifunctional (meth)acrylate
monomer,
(D) a photopolymerization initiator,
(E) a benzotriazole anticorrosive agent,
(F) an anticorrosive pigment selected from a phosphate
anticorrosive pigment and calcium ion-exchanged silica, and
(G) a phosphate ester.
Some preferred embodiments of a photocurable composition according
to the present invention has the following features: the phosphate
ester (G) is a (meth)acrylate having a phosphate group in its
molecule; the photocurable (meth)acrylate resin (A) is at least one
member selected from the group consisting of a polyester
(meth)acrylate, an epoxy (meth)acrylate, a polyether
(meth)acrylate, and a polyurethane (meth)acrylate; the composition
contains, in mass parts, 5-50 parts of component (A), 5-50 parts of
component (B), 5-30 parts of component (C), 1-15 parts of component
(D), 0.1-5 parts of component (E), 1-10 parts of component (F), and
1-5 parts of component (G), wherein the sum of components (A)-(G)
is 100 parts by mass; it further contains (H) a lubricant; and it
further contains (I) a fluorescent brightening agent.
The present invention also provides: use of the above-described
photocurable composition as a material for forming a
rust-preventing coating for a threaded joint for steel pipes; a
photocured coating formed from the photocurable composition; the
above-described photocured coating having a turbidity of at most
40%; a substrate with a photocured coating having the
above-described photocured coating; a threaded joint for steel
pipes with a photocured coating having the above-described
photocured coating on the surface of a pin and/or a box of a
threaded joint for steel pipes; a rust-preventing method for a
threaded joint for steel pipes comprising the steps of applying the
above-described photocurable composition to the surface of a pin
and/or a box of a threaded joint for steel pipes and then
irradiating the coated surface with active energy rays to cure the
applied composition and form a photocured coating; and a method of
manufacturing a threaded joint for steel pipes with a photocured
coating comprising the steps of applying the above-described
photocurable composition to the surface of a pin and/or a box of a
threaded joint for steel pipes and then irradiating the coated
surface with active energy rays to cure the applied composition and
form a photocured coating.
A photocurable composition according to the present invention can
form a photocured coating (hereinafter referred to as a photocured
coating of the present invention) which has excellent properties in
terms of gastightness, adhesion to a substrate, lubricating
properties, galling resistance, and corrosion resistance and which
is a thin film with high transparency on the surface of a substrate
and particularly on the surface of a threaded joint for steel pipes
and particularly for oil country tubular goods. The lubricating
properties and corrosion resistance which the photocured coating of
the present invention exhibits are comparable to those of a
compound grease and a storage grease.
As a result, the present invention can achieve the following
effects.
(1) It is not necessary to use a compound grease or a storage
grease at the time of forming a coating on a threaded joint or at
the time of makeup, thereby eliminating adverse effects on the
environment and humans caused by the use of such a grease.
(2) A threaded joint having a photocured coating of the present
invention has excellent corrosion resistance. Therefore, even when
oil country tubular goods are connected after a long period of
storage, it is not necessary to perform any special restoration
treatment and a threaded joint can be used as is.
(3) A threaded joint having a photocured coating of the present
invention can be inspected to check the threaded portion thereof
for damage while it maintains the photocured coating because the
coating is thin and has high transparency. Therefore, it is not
necessary to peel off the coating before inspection.
(4) Steel pipes (and particularly oil country tubular goods) are
exported to regions which experience high temperatures, regions
which are extremely cold in winter, and regions which have severe
variations between hot and cold in the day and night. Therefore, a
coating formed on a threaded joints for steel pipes is required to
have adhesion to a substrate such that it does not peel off the
substrate even in an environment having repeated high and low
temperatures. A photocured coating of the present invention
satisfies such demands. Accordingly, the coating does not peel off
when a threaded joint is actually made up, and the lubricating
properties of the joint during makeup do not deteriorate.
(5) A photocured coating of the present invention has a surface
with good lubricating properties (or a low coefficient of
friction). As a result, when a pin of a threaded joint for steel
pipes is inserted into a box, the threaded joint can be smoothly
tightened without cross threading of the male and female threads
and without damage of a thread by a mating thread.
(6) A photocured coating of the present invention does not
interfere with the galling resistance of a lubricant or a
lubricating coating normally used when connecting steel pipes.
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is a schematic view of the pin-box structure of a typical
threaded joint used for connecting oil country tubular goods.
EMBODIMENTS OF THE INVENTION
Below, a photocurable composition and uses thereof (such as a
photocured coating, a substrate with a photocured coating, and a
threaded joint for steel pipes having a photocured coating), a
rust-preventing method for a threaded joint for steel pipes using
this photocurable composition, and a method of manufacturing a
threaded joint for steel pipes having a photocured coating will be
explained in detail together with preferred modes thereof. A
photocurable composition according to the present invention is
particularly suitable as a material for forming a rust-preventing
coating for a threaded joint for steel pipes.
In the present invention, various terms have the following
definitions.
A pin refers to a joint component having male threads. For example,
it is a joint component having male threads formed on the ends of
an oil country tubular good. A box refers to a joint component
having female threads. For example, it is a joint component having
female threads formed on the inner surface of a threaded joint
member (a coupling).
A threaded joint for steel pipes is a typical threaded joint used
for connection of steel pipes (such as oil country tubular goods).
A typical threaded joint for steel pipes used for connecting oil
country tubular goods has a pin-box structure. Unthreaded metal
contact portions are formed close to the distal end of the male
threads of the pin and close to the proximal end of the female
threads of the box. Gastightness of a threaded joint can be
guaranteed by inserting one end of an oil country tubular good into
a threaded joint member and tightening the male threads and the
female threads until the unthreaded metal contact portions of the
pin and box contact each other and form a metal-to-metal seal.
Various types of threaded joints for steel pipes having this type
of pin-box structure include (1) a threaded joint for steel pipes
constituted by a steel pipe having a pin on the outer surface of
both of its ends and a threaded joint member (a coupling) which is
a separate connecting member from the steel pipe and which has a
box on its inner surface on both sides thereof, (2) a threaded
joint for a steel pipe constituted by a steel pipe having a box on
its inner surface at both of its ends and a threaded joint member
having a pin on its outer surface on both sides thereof, and (3) an
integral threaded joint constituted by a steel pipe having a pin
(which has male threads formed thereon) on the outer surface of one
end of the pipe and a box (having female threads formed thereon) on
the inner surface of its other end (namely, steel pipes are
directly connected to each other without using a threaded joint
member). Thus, a threaded joint for steel pipes collectively refers
to the combination of a steel pipe and a threaded connecting member
(above-described (1) and (2)) and individual steel pipes
(above-described (3)).
[Photocurable Composition]
A photocurable composition according to the present invention
comprises (A) a photocurable (meth)acrylate resin, (B) a
(meth)acrylate monomer selected from a monofunctional
(meth)acrylate monomer and a difunctional (meth)acrylate monomer,
(C) a trifunctional or higher multifunctional (meth)acrylate
monomer, (D) a photopolymerization initiator, (E) a benzotriazole
anticorrosive agent, (F) an anticorrosive pigment selected from a
phosphate anticorrosive pigment and calcium ion-exchanged silica,
and (G) a phosphate ester.
In addition, the photocurable composition may contain various
additives (such as (H) a lubricant and (I) a fluorescent
brightening agent) as optional components. In each of the
above-described essential components and optional components, one
member selected from the class of the component can be used singly,
or two or more members selected therefrom can be used in
combination.
The above-described components (A)-(G) of which the above-described
photocurable composition is comprised are all known substances, and
compositions which comprise some of these components have been
disclosed in the prior art. However, a coating formed from a
composition comprising some of these components did not necessarily
have a good balance between corrosion resistance and adhesion to a
substrate in an environment with repeated high and low
temperatures. In contrast, a photocurable composition according to
the present invention comprising the above-described components (A)
(G) as essential components has the following characteristics.
(1) Components (A), (B), and (C) are resinous film-forming
components in a photocurable composition according to the present
invention, and all of them are photopolymerizable. In other words,
a photocurable composition according to the present invention
contains substantially no resin components which do not undergo
photopolymerization. Therefore, the overall composition is rapidly
cured by irradiation with active energy rays and can form a coating
which as a whole has a uniform degree of cross linking. Such a
coating has excellent adhesion to a substrate even in an
environment with repeated high and low temperatures, and it has a
high degree of corrosion resistance.
(2) Due to the rust-preventing action of the benzotriazole
anticorrosive agent (E) and the anticorrosive pigment (F) selected
from a phosphate anticorrosive pigment and calcium ion-exchanged
silica with respect to a substrate metallic material, a photocured
coating of the present invention exhibits excellent corrosion
resistance which is comparable to that of compound grease and
storage grease. Accordingly, this coating has a good balance
between the finished external appearance, adhesion to a substrate
in an environment with repeated high and low temperatures, and
corrosion resistance. Each of these properties is particularly
important for a material which is used to form a rust-preventing
coating on a threaded joint for steel pipes. From this standpoint,
a photocurable composition according to the present invention is a
superior material for forming a rust-preventing coating on a
threaded joint for steel pipes compared to a conventional
composition.
(3) By using a benzotriazole anticorrosive agent (E), the surface
of a photocured coating of the present invention has improved
lubricating properties. Although the reason therefor is uncertain,
it is thought that a benzotriazole anticorrosive agent (E) is more
readily adsorbed by a substrate steel surface compared to other
components constituting the photocurable composition, so the
composition develops a concentration distribution which varies in
the thickness direction of the coating, as a result of which a
hardness gradient develops in the thickness direction of the
coating (the hardness decreases toward the substrate), and this
hardness gradient has a beneficial effect on lubricating
properties. On the other hand, it is thought that this hardness
gradient is not suitably obtained when one or more of the essential
components of a photocurable composition according to the present
invention is absent.
Below, each of the above-described components will be explained in
detail.
(A) Photocurable (Meth)Acrylate Resin
As the photocurable (meth)acrylate resin (A), for example, at least
one member selected from the group consisting of a polyester
(meth)acrylate, an epoxy (meth)acrylate, a polyether
(meth)acrylate, and a polyurethane (meth)acrylate is used.
An example of the polyester (meth)acrylate is a polyester
(meth)acrylate obtained by reacting (meth)acrylic acid with a
polyester prepared from a polybasic acid or an anhydride thereof
and a polyhydric alcohol. Examples of the polybasic acid include
phthalic acid, succinic acid, adipic acid, glutaric acid, sebacic
acid, isosebacic acid, tetrahydrophthalic acid, hexahydrophthalic
acid, dimer acid, trimellitic acid, pyromellitic acid, pimelic
acid, azelaic acid, and the like. Examples of the polyhydric
alcohol include 1,6-hexanediol, diethylene glycol, 1,2-propylene
glycol, 1,3-butylene glycol, neopentyl glycol, dipropylene glycol,
polyethylene glycol, polypropylene glycol, and the like.
An example of the epoxy (meth)acrylate (also referred to as an
epoxy (meth)acrylate resin) is a (meth)acrylic acid modified epoxy
resin obtained by adding (meth)acrylic acid to an epoxy resin or an
alicyclic epoxy resin. The epoxy resin which is subjected to
modification can be prepared, for example, by reacting bisphenol A,
bisphenol F, bisphenol S, or phenol novolak with epichlorohydrin.
The alicyclic epoxy resin which is subjected to modification can be
prepared, for example, by reacting cyclopentadiene oxide or
cyclohexene oxide with epichlorohydrin.
An example of the polyether (meth)acrylate is a polyether
(meth)acrylate obtained by an ester exchange reaction between a
polyether and a (meth)acrylate ester such as ethyl methacrylate.
Examples of the polyether include polyethers obtained by
ethoxylated or propoxylated trimethylolpropane, pentaerythritol or
the like, or polyetherification of 1,4-propanediol or the like.
An example of the polyurethane (meth)acrylate is a polyurethane
(meth)acrylate obtained by reacting an isocyanate compound, a
polyol compound and a hydroxy group-containing (meth)acrylate
compound. Examples of the isocyanate compound include tolylene
diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate,
isophorone diisocyanate, and the like. Examples of the polyol
compound include an adduct of hydrogenated bisphenol A and ethylene
oxide, hydrogenated bisphenol A, neopentyl glycol, 1,6-hexanediol,
trimethylolpropane, and the like. Examples of the hydroxy
group-containing (meth)acrylate compound include hydroxy
group-containing alkyl esters of (meth)acrylic acid such as
2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and
2-hydroxybutyl (meth)acrylate.
As the (meth)acrylate resin (A), a polyester (meth)acrylate, an
epoxy (meth)acrylate (a (meth)acrylic acid modified epoxy resin),
and a polyurethane (meth)acrylate are preferred.
Taking into consideration the coating hardness and viscosity of the
coating composition, the glass transition temperature (Tg) of the
(meth)acrylate resin (A) is usually from -30.degree. C. to
+200.degree. C. and preferably from -20.degree. C. to +160.degree.
C., and the average molecular weight (Mn) thereof is normally
500-200,000 and preferably 500-80,000. The viscosity at 25.degree.
C. of the (meth)acrylate resin (A) is normally 500-100,000 mPa-sec
and preferably 1000-80,000 mPa-sec.
The (meth)acrylate resin (A) can be prepared by suitably selecting
the starting monomers such that at least one recurring unit
selected from a recurring unit derived from (meth)acrylic acid and
a recurring unit derived from a (meth)acrylate ester is contained
in the molecule of the resulting resin and that the properties of
the resulting resin are within the above-defined ranges and by
polymerizing the selected starting monomers using a known technique
(e.g., solution free radical polymerization).
Examples of the starting monomers include (meth)acrylic acid and
(meth)acrylate esters which are normally used. The (meth)acrylate
ester includes alkyl esters of (meth)acrylic acid (in which the
alkyl contains 1-18 carbon atoms) and cycloalkyl esters of
(meth)acrylic acid (in which the cycloalkyl contains 3-8 carbon
atoms). Specific examples of the (meth)acrylate ester include
methyl, ethyl, n-propyl, isopropyl, butyl (n-, i-, t-), hexyl,
2-ethylhexyl, n-octyl, decyl, lauryl, stearyl, and cyclohexyl
esters of (meth)acrylic acid. Among these, methyl (meth)acrylate,
ethyl (meth)acrylate, and butyl (meth)acrylate are preferred.
Other monomers which can be copolymerized with (meth)acrylic acid
or the above-described (meth)acrylate esters can be used as a
starting monomer. Examples of other monomers are alkoxy alkyl
esters of (meth)acrylic acid (the alkoxy alkyl having 2-18 carbon
atoms) such as methoxyethyl (meth)acrylate, methoxybutyl
(meth)acrylate, and ethoxybutyl (meth)acrylate; aminoalkyl esters
of (meth)acrylic acid such as N,N-dimethylaminoethyl (meth)acrylate
and N,N-dimethylaminopropyl (meth)acrylate; and hydroxy
group-containing alkyl esters of (meth)acrylic acid such as
2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and
hydroxybutyl (meth)acrylate.
Macromonomers such as the above-described polyester (meth)acrylate,
epoxy (meth)acrylate, polyether (meth)acrylate, and polyurethane
(meth)acrylate can also be used as the starting monomer.
(B) (Meth)Acrylate Monomer Selected from Monofunctional
(Meth)Acrylate Monomers and Difunctional (Meth)Acrylate
Monomers
Each of a monofunctional (meth)acrylate monomer and a difunctional
(meth)acrylate monomer (B) and a trifunctional or higher
multifunctional (meth)acrylate monomer (C) undergoes
photopolymerization and constitutes a portion of the resulting
polymer. These monomers also function as a diluting agent of the
photocurable (meth)acrylate resin (A) when preparing the
photocurable composition, thereby improving the applicability of
the composition and enabling the preparation of a solvent-free
coating composition.
As each of these (meth)acrylate monomers, it is preferable to use a
monomer which has good reactivity (such as the ability to
copolymerize) with the photocurable (meth)acrylate resin and a high
curing rate. As the component (B), either a monofunctional
(meth)acrylate mononer or a difunctional (meth)acrylate monomer can
be used alone, or both of them can be used in combination.
Examples of the monofunctional (meth)acrylate monomer include
2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate,
ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, methyltriglycol (meth)acrylate,
isodecyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl
(meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, lauryl
(meth)acrylate, and the like.
As the difunctional (meth)acrylate monomer, for example, at least
one member selected from an aliphatic di(meth)acrylate, an
aliphatic di(meth)acrylate having an ether linkage, an alicyclic
di(meth)acrylate, an aromatic di(meth)acrylate, and derivatives of
these compounds can be used.
Examples of the aliphatic di(meth)acrylate include
1,3-butyleneglycol di(meth)acrylate, 1,4-butanediol
di(meth)acrylate (BDDA, 1,4-butyleneglycol di(meth)acrylate),
neopentylglycol di(meth)acrylate (NPGDA), hydroxypivalic acid
neopenty glycol di(meth)acrylate (HPNDA), 1,6-hexanediol
di(meth)acrylate (HDDA, 1,6-hexyleneglycol di(meth)acrylate), and
the like.
Examples of the aliphatic di(meth)acrylate having an ether linkage
include diethyleneglycol di(meth)acrylate (DEGDA),
tetraethyleneglycol di(meth)acrylate (TEGDA), polyethylene glycol
400 di(meth)acrylate (PEG400DA), tripropyleneglycol
di(meth)acrylate (TPGDA), and the like.
Examples of the alicyclic di(meth)acrylate include dicyclopentanyl
di(meth)acrylate and the like. Examples of the aromatic
di(meth)acrylate include bisphenol A diglycidyl ether
di(meth)acrylate and the like.
Among these, a monofunctional (meth)acrylate monomer, an aliphatic
di(meth)acrylate, and an aliphatic di(meth)acrylate having an ether
linkage are preferred as component (B).
(C) Trifunctional or Higher Multifunctional (Meth)Acrylate
Monomer
The trifunctional or higher multifunctional (meth)acrylate monomer
(C) is a (meth)acrylate monomer having at least three and
preferably 3-6 polymerizable unsaturated groups such as
(meth)acryloyl groups or (meth)acryloyloxy group per molecule.
The trifunctional or higher multifunctional (meth)acrylate monomer
(C) can be prepared, for example, by reacting a compound having
three or more hydroxyl groups in the molecule with a (meth)acrylic
acid or a (meth)acrylic acid derivative having a carboxyl group at
a ratio of at least 3 moles of the latter to 1 mole of the
former.
Specific examples of a trifunctional (meth)acrylate monomer include
trimethylolpropane tri(meth)acrylate (TMPTA),
trimethylolpropaneethoxy tri(meth)acrylate,
trimethylolpropanepropoxy tri(meth)acrylate, pentaerythritol
tri(meth)acrylate (PETA), glycerinepropoxy tri(meth)acrylate
(GPTA), and the like.
(D) Photopolymerization Initiator
Any known photopolymerization initiator can be used as component
(D). A preferred photopolymerization initiator (D) includes
benzoin, benzoin methyl ether, benzoin isopropyl ether, benzoin
isobutyl ether, .alpha.-acrylbenzoin, benzil, benzophenone,
2-ethylanthraquinone, 1-chloroanthraquinone,
2-chloroanthra-quinone, thioxanthone, chlorothioxanthone,
2-methylthioxanthone, 2-hydroxy-2-methylpropiophenone,
2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl
ketone, 2-methyl-[4-(methyl)thiophenyl]-2-morpholino-1-propanone,
and the like.
(E) Benzotriazole Anticorrosive Agent
Examples of the benzotriazole anticorrosive agent (E) include
ethylbenzotriazole, benzotriazole butyl ester, benzotriazole methyl
ester, chlorobenzotriazole, 1-hydroxymethylbenzotriazole,
1-(2,3-dihydroxypropyl)-benzotriazole,
1-(1,2-dicarboxyethyl)benzotriazole,
1-[N,N-bis(2-ethylhexyl)-aminomethyl]benzotriazole,
1,2,3-benzotriazole, carboxybenzotriazole, and the like. Among
these, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole and
1,2,3-benzotriazole are preferred from the standpoint of
rust-preventing effect and suitability for a coating
composition.
(F) Anticorrosive Pigment
A photocurable coating composition according to the present
invention contains an anticorrosive pigment (F) selected from a
phosphate anticorrosive pigment and calcium ion-exchanged
silica.
As the phosphate anticorrosive pigment, at least one member
selected from an aluminum salt, a magnesium salt, a calcium salt,
and a zinc salt of phosphoric acid, phosphorous acid,
polyphosphoric acid, or phosphomolybdic acid can be used. The
calcium ion-exchanged silica is a non-toxic anticorrosive pigment
in which calcium ions are incorporated by ion exchange into a
silica support having a fine porous structure. Either a phosphate
anticorrosive pigment or calcium ion-exchanged silica can be used
alone, or both of them can be used in combination.
The mean primary particle diameter of the anticorrosive pigment (F)
selected from a phosphate anticorrosive pigment and calcium
ion-exchanged silica is preferably at least 1 .mu.m and not greater
than 10 .mu.m from the standpoints of dispersibility in the coating
composition and the external appearance and transparency of the
coating. The mean primary particle diameter can be measured by the
electrical resistance method.
In a photocurable coating composition according to the present
invention, a benzotriazole anticorrosive agent (E) and an
anticorrosive pigment (F) selected from a phosphate anticorrosive
pigment and calcium ion-exchanged silica are used in combination.
As a result, due to the chelating action of the benzotriazole
anticorrosive agent (E) and the sacrificial anodic action of the
phosphate anticorrosive pigment (F) and/or the ion exchange action
of the calcium ion-exchanged silica, it is possible to form a
photocured coating having excellent corrosion resistance which is
comparable to that obtained with compound grease or storage
grease.
(G) Phosphate Ester
A photocurable composition according to the present invention
contains a phosphate ester (G) particularly in order to improve the
adhesion of a photocured coating formed therefrom to a
substrate.
The phosphate ester (G) is preferably a photocurable compound from
the standpoint of maintaining a high level of adhesion to the
substrate of the photocured coating for long periods. More
preferably, it contains at least one ethylenically unsaturated bond
in the molecule. Examples of the phosphate ester (G) include alkyl
phosphates which contain at least one ethylenically unsaturated
bond in the molecule, aralkyl phosphates which contain at least one
ethylenically unsaturated bond in the molecule, allyl phosphate,
(meth)acrylates having a phosphate group in the molecule (referred
to below as (meth)acrylate phosphates), and the like.
Among these, a (meth)acrylate phosphate is preferred. Examples of a
(meth)acrylate phosphate are compounds having the following formula
(1) or (2).
##STR00001##
In formulas (1) and (2), R stands for
CH.sub.2.dbd.CR.sup.1--COO--R.sup.2--O--, R.sup.1 stands for H or
CH.sub.3, and R.sup.2 stands for a straight chain or branched
alkylene group having 1-4 carbon atoms. In formula (I), the two R's
may be the same or different from each other.
By using the (meth)acrylate phosphate of formula (1) or (2), the
adhesion of the photocured coating to the substrate is improved due
to a reaction between the phosphate group and the surface of the
substrate (metal).
Specific examples of the (meth)acrylate phosphate include
2-hydroxy-ethyl (meth)acrylate phosphate (also referred to as
2-(meth)acryloyloxyethyl acid phosphate), (meth)acryloyloxyethyl
phosphorylphenyl, EO (ethylene oxide)-modified (meth)acrylate
phosphate, EO-modified phenoxylated (meth)acrylate phosphate,
EO-modified butoxylated (meth)acrylate phosphate, EO-modified
octoxylated (meth)acrylate phosphate, and the like.
Various Additives
In addition to the above-described essential components (A) to (G),
a photocurable composition according to the present invention may
contain as optional components various additives which are commonly
used in the field of coating compositions. Examples of such
additives include (H) a lubricant and (I) a fluorescent brightening
agent.
Examples of the lubricant (H) include waxes such as polyethylene
wax, paraffin wax, and carnauba wax; solid lubricants such as
polytetrafluoroethylene (PTFE); and the like. Among these,
polyethylene wax is preferred from the standpoints of maintaining
lubricating properties over long periods and cost.
A photocurable composition according to the present invention can
form a photocured coating having satisfactory lubricating
properties even if it does not contain any lubricant (H). However,
addition of the lubricant (H) can provide the photocured coating
with further improvement in lubricating properties (slipping
properties). Therefore, in accordance with the lubricity demanded
of the photocured coating, if necessary, the lubricant (H) can be
added to the photocurable composition. For example, when the
substrate is a threaded joint for steel pipes, it is possible to
further improve the lubricity of the threaded joint by addition of
the lubricant (H).
The fluorescent brightening agent (I) can be added to a
photocurable composition, if necessary, in order to improve the
visibility of a photocured coating formed from the composition.
Examples of the fluorescent brightening agent (I) include compounds
such as benzoxazoles, oxazoles, stilbenes, coumarins, pyrazolines,
imidazoles, naphthalimides, bisbenzoxazoles, and
bis-styrylbiphenyls; diaminostilbene disulfonic acid derivatives,
and the like. Among these, bisbenzoxazole compounds are preferred,
and 2,5-thiophenediyl-bis(5-tert-butyl-1,3-benzoxazole), which is
the compound represented by the following formula 3, is more
preferred.
##STR00002##
Proportion of Each Component of a Photocurable Composition
A photocurable composition according to the present invention
preferably contains the respective components in proportions within
the following ranges, which are indicated in parts by mass, with
the sum of components (A) to (G) being 100 parts:
5-50 parts of component (A),
5-50 parts of component (B),
5-30 parts of component (C),
1-15 parts of component (D),
0.1-5 parts of component (E),
1-10 parts of component (F), and
1-5 parts of component (G).
The proportion of each component of a photocurable composition is
indicated as its dry solids content (exclusive of the content of
solvent, if any). When the content of each of components (A) to (G)
is within the above-described range, a photocured coating formed
from the composition has a good balance between adhesion to the
substrate and corrosion resistance.
A more preferred proportion of each component is in the following
range:
20-40 parts of component (A),
20-40 parts of component (B),
10-25 parts of component (C),
3-10 parts of component (D),
0.3-3 parts of component (E),
3-8 parts of component (F), and
2-4 parts of component (G).
From the standpoints of balancing adhesion to the substrate and
corrosion resistance, it is also preferred that the content of each
of the above components with respect to 1 part of component (C) be
in the following range:
0.8-4 parts of component (A),
0.8-4 parts of component (B),
0.1-1 parts of component (D),
0.02-0.3 parts of component (E),
0.12-0.8 parts of component (F), and
0.08-0.4 parts of component (G).
When a photocurable composition according to the present invention
contains a lubricant (H), the content of the lubricant (H) is
preferably 0.1-5 percent by mass and more preferably 0.1-3 percent
by mass based on the total amount of the photocurable composition.
In addition, the lubricant (H) is preferably used in an amount of
0.1-10 parts and more preferably 0.1-5 parts by mass with respect
to 100 parts of the total amount of components (A)-(G) in the
photocurable composition. If the content of the lubricant (H) is
too low, when the photocurable composition is applied to a threaded
joint for steel pipes and cured to form a rust-preventing coating,
the desired further improvement in the lubricity (lubricating
properties) of the threaded joint may not be achieved. If the
content of the lubricant (H) is too high, it can result in
inadequate curability and a decrease in the adhesion between the
coating and a substrate.
When a photocurable composition contains a fluorescent brightening
agent (I), its content is preferably 0.1-3 percent by mass and more
preferably 0.1-1 percent by mass based on the total amount of the
photocurable composition. In addition, the fluorescent brightening
agent (I) is preferably used in an amount of 0.1-5 parts and more
preferably 0.1-3 parts by mass with respect to 100 parts of the
total of components (A)-(G) in the photocurable composition. If the
content of the fluorescent brightening agent (I) is too low, the
intended effect of adding the fluorescent brightening agent (I) may
not be sufficiently exhibited. If the content of this component is
too high, it sometimes leads to poor curability and a decrease in
adhesion between the coating and a substrate.
[Formation of a Rust-Preventing Coating on a Threaded Joint for
Steel Pipes]
A photocurable composition according to the present invention can
be suitably used as a material for forming a rust-preventing
coating on a threaded joint for steel pipes (referred to below
simply as a coating composition). By using this coating
composition, a rust-preventing coating having excellent corrosion
resistance and excellent adhesion with respect to a substrate in
the form of a threaded joint for steel pipes can be formed.
In this case, the photocurable composition may contain, in addition
to the above-described components, small amounts (e.g., at most 10%
by mass of the overall composition) of additives which have
conventionally been used in a coating composition as optional
components as long as they do not have a significant adverse action
on the objects and effects of the present invention. It is expected
that these additives may further improve the performance and
quality of the photocurable composition as a coating
composition.
Examples of the additives which can be used include an amine- or
quinone-type photopolymerization promoter, a thermal polymerization
inhibitor, an inorganic filler, an organic filler, an adhesion
imparting agent, a thixotropic agent, a plasticizer, a nonreactive
polymer, a coloring pigment, an anti-settling agent, an antifoaming
agent, a leveling agent, and the like.
If desired, an anticorrosive agent other than the benzotriazole
anticorrosive agent (E) and the anticorrosive pigment (F) selected
from a phosphate anticorrosive pigment and calcium ion-exchanged
silica may be added as long as it does not markedly increase the
turbidity of the coating or markedly decrease the coating
curability. Examples of such an anticorrosive agent include
molybdic acid calcium or aluminum salt, boric acid barium or
calcium salt, calcium silicate, calcium borosilicate, and the
like.
[Method of Preparing a Photocurable Composition or a Coating
Composition]
A photocurable composition and a coating composition according to
the present invention can be prepared in a conventional manner. For
example, the above-described components which have been weighed to
give proportions in the above-described ranges can be mixed and
dispersed using a dispersion mixer such as a ball mill, a bead
mill, or a three-roll mill, or a stirring mixer such as a high
speed rotating blade mixer called a disper mixer to prepare the
above-described photocurable composition or coating
composition.
A photocurable composition and a coating composition according to
the present invention does not substantially contain and does not
need to contain powders of heavy metals such as zinc, lead, or
copper which are contained in large amounts in a conventional
rust-preventing coating for a threaded joint for steel pipes.
Therefore, adverse effects of these powders on the environment and
humans can be avoided when forming or using a photocured
coating.
[Substrate to be Coated]
Examples of substrates which can be coated with a photocurable
composition and a coating composition according to the present
invention include plates or sheets, wires, rods, pipes, and various
other metal substrates (shaped members). Examples of metals which
constitute the above-described substrates are various metals such
as iron, carbon steel, copper, zinc, tin, and aluminum; and alloys
of these metals. The substrate may be a material plated with such a
metal or alloy. Since a photocurable composition and a coating
composition according to the present invention can form a coating
having excellent corrosion resistance, they are particularly suited
for carbon steel and alloy steels having a Cr content of at most 20
mass percent. A photocurable composition and a coating-forming
material according to the present invention can also be applied to
the above-described various substrates (shaped members) and used
for applications other than rust prevention.
Among these uses, a photocurable composition and a coating
composition according to the present invention are suitable for use
to form a coating intended for rust prevention or rust prevention
and lubrication on a threaded joint for pipes and particularly on
the pin and/or the box of a threaded joint for steel pipes.
[Photocured Coating, Substrate with a Photocured Coating, and
Threaded Joint for Steel Pipes Having a Photocured Coating]
A photocured coating according to the present invention is formed
from the above-described photocurable composition. The photocured
coating is usually formed on the above-described substrate (such as
the contact surfaces of a threaded joint for steel pipes). The
method for its formation is as described later.
A substrate having a photocured coating according to the present
invention has the above-described photocured coating on a surface
of a metal substrate.
A threaded joint for steel pipes having a photocured coating
according to the present invention is characterized by having the
above-described photocured coating on the surface of a pin and/or a
box of a threaded joint for steel pipes. The photocured coating has
excellent corrosion resistance and adhesion to a substrate in the
form of the threaded joint for pipes.
The thickness of the photocured coating is normally in the range of
1-100 micrometers. Taking into consideration the cost for rust
prevention, corrosion resistance, ease of makeup, and the curing
efficiency of the photocurable composition, the coating thickness
is preferably 5-30 micrometers.
The photocured coating has good adhesion to a substrate (such as
the contact surfaces of a threaded joint for steel pipes). For
example, the photocurable composition does not peel off a substrate
even if there is an external impact at the time of transport or
handling or contact with a roll skid or the like. The photocurable
composition also has excellent corrosion resistance
(rust-preventing properties).
A photocured coating according to the present invention is highly
transparent, so it is possible to optically inspect threaded
portions of a threaded joint for damage from above the coating.
Specifically, the turbidity of the photocured coating is preferably
at most 40% and more preferably at most 15%. As the turbidity
increases, the transparency decreases, and it sometimes becomes
difficult to ascertain whether there is damage to threaded
portions. The lower the turbidity of the photocured coating the
better. The lower limit of the turbidity is usually 0.1%. A method
of measuring turbidity is described in the following example.
The turbidity of the photocured coating can be adjusted by the
proportions of pigment components such as an anticorrosive pigment
(such as the anticorrosive pigment (F) selected from a phosphate
anticorrosive pigment and calcium ion-exchanged silica) and the
lubricant (H). The turbidity increases as the proportions of these
components increase.
[Method for Rust Prevention of a Threaded Joint for Steel Pipes and
Method of Manufacturing a Threaded Joint for Steel Pipes Having a
Photocured Coating]
A method for rust prevention of a threaded joint for steel pipes
according to the present invention (a method of surface treatment
for rust prevention) comprises the steps of applying the
above-described photocurable composition to the surfaces of a pin
and/or a box of a threaded joint for steel pipes and then
irradiating the coated surfaces with active energy rays to cure the
composition and form a photocured coating.
A method of manufacturing a threaded joint for steel pipes having a
photocured coating according to the present invention comprises the
steps of applying the above-described photocurable composition to
the surfaces of a pin and/or a box of a threaded joint for steel
pipes and then irradiating the coated surfaces with active energy
rays to cure the composition and form a photocured coating.
The contact surfaces of the threaded joint for pipes (the surfaces
of the threaded portions and the unthreaded metal contact portions
of the pin and/or the box of the threaded joint) can be irradiated
with active energy rays immediately after the application of the
above-described photocurable composition, and the composition as a
whole is rapidly cured by photopolymerization, thereby forming a
coating with uniform degree of cross linking. This uniform coating
has good adhesion to the surface of a steel pipe and can
effectively prevent the formation of rust.
Prior to applying the photocurable composition, the surface of the
steel pipe may be subjected to chemical conversion treatment known
in the art such as oxalate or phosphate chemical conversion
treatment to form a primary or undercoating as a means for
assisting in rust prevention and improving the adhesion of the
coating. The surface may also be subjected to surface roughening
treatment known in the art such as shot blasting and shot peening
for the purpose of improving the adhesion of the coating. In
addition, it is preferable to adequately remove moisture and oil
remaining on the surface of the steel pipe prior to application of
the photocurable composition. As long as the object and effects of
they present invention are not impaired, a conventional known
lubricant may be applied atop the photocured coating, or a
conventional known lubricating coating or anticorrosive coating may
be formed atop the photocured coating.
Spraying, showering, dipping, roll application, or the like can be
used as a method of applying the photocurable composition and the
coating composition to form a rust-preventing coating on a threaded
joint for steel pipes.
As a source of active energy rays, it is convenient to use a device
capable of generating ultraviolet light such as an (ultra) high
pressure mercury lamp or a metal halide lamp, but it is also
possible to use an electron beam accelerator, cobalt 60 as a source
of gamma rays, or the like. It is convenient to use a "continuous
coating system to form a rust-preventing coating on a threaded
joint for pipes" in which a steel pipe which is being transported
by rollers is successively subjected to application of the
photocurable composition and irradiation with active energy
rays.
EXAMPLES
The present invention will be explained by the following examples
but the present invention is not limited to these examples. In the
following examples and comparative examples, unless otherwise
specified, "parts" means parts by mass.
[Methods for Measuring Tg, Mn, and Viscosity of a Photocurable
(Meth)Acrylate Resin]
Tg: Measured with a differential scanning calorimeter (DSC) in
accordance with JIS K7121; Mn: Measured by gel permeation
chromatography (GPC); Viscosity: Measured with a Brookfield
viscometer in accordance with JIS K7117-2.
Example 1
In order to prepare the composition shown in Table 1, the following
components (100 parts in total) were added to a vessel in
appropriate order and stirred using a disper mixer into a uniform
mixture to form a photocurable composition:
20 parts of a photocurable acrylate resin (SHIKO.TM. UV3200B,
Nippon Synthetic Chemical Industry Co., Ltd.),
20 parts of a photocurable acrylate resin (RIPDXY.TM. VR-77-80TPA,
Showa Highpolymer Co., Ltd.),
8 parts of a monofunctional acrylate monomer (FANCRYL.TM. FA-512A,
Hitachi Chemical Co., Ltd.),
13 parts of a difunctional monomer (TPGDA, Daicel-Cytec Co.,
Ltd.),
5 parts of a difunctional monomer (VISCOAT.TM. #215, Osaka Organic
Chemical Industry Ltd.),
15 parts of a trifunctional monomer (NEW FRONTIER.TM. TMPT,
Dai-ichi Kogyo Seiyaku, Co., Ltd.),
7 parts of a photopolymerization initiator (IRGACURE.TM. 184, Ciba
Specialty Chemicals),
3 parts of a photopolymerization initiator (IRGACURE.TM. 651, Ciba
Specialty Chemicals),
1 part of a benzotriazole anticorrosive agent (BT-LX, Johoku
Chemical Co., Ltd.),
5 parts of a phosphate anticorrosive pigment (EXPERT.TM. NP-1102,
Toho Ganryo Kogyo Co. Ltd.), and
3 parts of a phosphate ester (LIGHTESTER.TM. P-2M, Kyoeisha
Chemical Co. Ltd.).
Using the photocurable composition, the following evaluations 1-4
were performed. The results are shown in Table 2.
Examples 2-10 and Comparative Examples 1-6
Photocurable compositions were prepared in the same manner as in
Example 1 except that the components shown in Table 1 were used in
the indicated proportions. The following evaluations 1-4 were
carried out on each of the resulting photocurable compositions. The
results are shown in Table 2.
The details of each of the components shown in Table 1 were as
follows.
[Components (A): Photocurable (Meth)Acrylate Resins]
A-1: a polyurethane acrylate from Nippon Synthetic Chemical
Industry Co., Ltd.: SHIKO.TM. UV3200B, Tg=-8.degree. C., Mn=10,000,
viscosity=50,000 mPa-sec (25.degree. C.);
A-2: a polyester acrylate from DIC Corp.: UNIDIC.TM. V3021, Mn=500,
viscosity=7,000 mPa-sec (25.degree. C.);
A-3: a polyester acrylate from Daicel-Cytec Co., Ltd.: EBECRYL.TM.
525, Mn=1000, viscosity=40,000 mPa-sec (25.degree. C.);
A-4: a polyester acrylate from Daicel-Cytec Co., Ltd.: EBECRYL.TM.
811, viscosity=1850 mPa-sec (60.degree. C.);
A-5: an epoxy acrylate from DIC Corp.: UNIDIC.TM. V5502, Tg=from
100-140.degree. C., Mn=1300, viscosity=2000 mPa-sec (25.degree.
C.);
A-5: an epoxy acrylate from Showa Highpolymer Co., Ltd.: RIPDXY.TM.
VR-77-80TPA, Mn=500, viscosity=40,000 mPa-sec (25.degree. C.).
[Components (B): Monofunctional or Difunctional (Meth)Acrylate
Monomers]
B-1: a monofunctional acrylate monomer--dicyclopentenyloxyethyl
acrylate from Hitachi Chemical Co., Ltd.: FANCRYL.TM. FA-512A;
B-2: a monofunctional acrylate monomer--phenoxyethyl acrylate from
Dai-ichi Kogyo Seiyaku Co., Ltd.: NEW FRONTIER.TM. PHE;
B-3: a difunctional acrylate monomer--tripropylene glycol
diacrylate from Daicel-Cytec Co., Ltd.: TPGDA;
B-4: a difunctional acrylate monomer--neopentylglycol diacrylate
from Osaka Organic Chemical Industry, Ltd.: VISCOAT.TM. #215;
B-5: a difunctional acrylate monomer--1,6-hexanediol diacrylate
from Dai-ichi Kogyo Seiyaku Co., Ltd: NEW FRONTIER.TM. HDDA.
[Components (C): Trifunctional or Higher Multifunctional
(Meth)Acrylate Monomers]
C-1: a trifunctional acrylate monomer--trimethylolpropane
triacrylate from Dai-ichi Kogyo Seiyaku Co., Ltd: NEW FRONTIER.TM.
TMPT;
C-2 a trifunctional acrylate monomer--pentaerythritol triacrylate
from Dai-ichi Kogyo Seiyaku Co., Ltd.: NEW FRONTIER.TM. PET-3.
[Components (D): Photopolymerization Initiators]
D-1: 1-hydroxycyclohexyl phenyl ketone from Ciba Specialty
Chemicals: IRGACURE.TM. 184;
D-2: 2,2-dimethoxy-2-phenylacetophenone from Ciba Specialty
Chemicals: IRGACURE.TM. 651.
[Component (E): a Benzotriazole Anticorrosive Agent]
E-1: 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole from Johoku
Chemical Co., Ltd.: BT-LX.
[Components (F): Anticorrosive Pigments]
F-1: a phosphate anticorrosive pigment--aluminum phosphite from
Toho Ganryo Co., Ltd.: EXPERT.TM. NP-1102;
F-2: calcium ion-exchanged silica (amorphous silicon dioxide and
calcium hydroxide) from Fuji Silysia Chemical Ltd.: SYLOMASK.TM.
55.
[Component (G): Phosphate Ester]
G-1: 2-methacryloyloxyethyl acid phosphate from Kyoeisha Chemical
Co., Ltd.: LIGHTESTER.TM. P-2M.
[Component (H): Lubricant]
H-1: micronized polyethylene wax from BYK Chemie: CERAFLOUR.TM.
991
[Component (I): Fluorescent Brightening Agent]
I-1: Fluorescent brightening
agent-2,5-thiophenediyl-bis(5-tert-butyl-1,3-benzoxazole from Ciba
Specialty Chemicals: TINOPAL.TM. OB.
TABLE-US-00001 TABLE 1 Photocurable composition (numerals in
examples indicate content in mass %) Examples Component Symbol
Chemical Name 1 2 3 4 5 6 7 8 (A) Photocurable A-1 Polyurethane
acrylate 20 15 20 15 (meth)acrylate resin A-2 Polyester acrylate 25
20 A-3 Polyester acrylate 36 20 A-4 Polyester acrylate 35 A-5 Epoxy
acrylate 13 20 A-6 Epoxy acrylate 20 15 10 15 15 (B) Mono- and di-
Mono B-1 Dicyclopentenyloxyethyl acrylate 8 32 20 8 8 functional
B-2 Phenoxyethyl acrylate 15 10 (meth)acrylate Di B-3 Tripropylene
glycol diacrylate 13 30 13 13 monomer B-4 Neopentylglycol
diacrylate 5 15 5 5 B-5 1,6-Hexanediol diacrylate 3 10 (C)
Trifunctional or higher C-1 Trimethylolpropane triacrylate 15 6 15
15 15 15 multifunctional (meth)acrylate C-2 Pentaerythritol
triacrylate 10 13 monomer (D) Photopolymerization D-1
1-Hydroxycyclohexyl phenyl ketone 7 7 7 7 7 7 7 7 intiator D-2
2,2-dimethoxy-2-phenylacetophenone 3 3 3 3 3 3.5 3 3 (E)
Benzotriazole E-1 1-[N,N-bis(2-ethylhexyl)aminomethyl]- 1 1 1 1 1 1
1 - 1 anticorrosive agent benzotriazole (F) Phosphate F-1 Aluminum
phosphite 5 5 5 5 5 5 10 15 Anticorrosive Ca F-2 Amorphous silicon
dioxide, pigment exchanged calcium hydroxide silica (G) Phosphate
ester G-1 2-methacryloyloxyethyl acid phosphate 3 3 3 3 3 3 3 3 (H)
Lubricant H-1 Micronized polyethylene wax 1 (I) Fluorescent
whitening I-1 2,5-thiophenediylbis(5-tert-butyl-1,3- 0.5 agent
benzoxazole) Total 100 100 100 100 100 100 100 100 Photocurable
composition (numerals in examples indicate content in mass %)
Examples Comparative Examples Component Symbol Chemical Name 9 10 1
2 3 4 5 6 (A) Photocurable A-1 Polyurethane acrylate 35 35 21 25 23
(meth)acrylate resin A-2 Polyester acrylate 20 A-3 Polyester
acrylate 35 A-4 Polyester acrylate A-5 Epoxy acrylate 31 20 20 20
20 A-6 Epoxy acrylate 15 (B) Mono- and di- Mono B-1
Dicyclopentenyloxyethyl acrylate 26 30 8 8 8 8 8 functional B-2
Phenoxyethyl acrylate 13 (meth)acrylate Di B-3 Tripropylene glycol
diacrylate 20 13 13 13 13 monomer B-4 Neopentylglycol diacrylate 5
5 5 5 5 B-5 1,6-Hexanediol diacrylate (C) Trifunctional or higher
C-1 Trimethylolpropane triacrylate 15 15 15 15 15 multifunctional
(meth)acrylate C-2 Pentaerythritol triacrylate 15 15 20 monomer (D)
Photopolymerization D-1 1-Hydroxycyclohexyl phenyl ketone 7 7 7 7 7
7 7 7 intiator D-2 2,2-dimethoxy-2-phenylacetophenone 3 3.5 3 3 3 3
3 3 (E) Benzotriazole E-1 1-[N,N-bis(2-ethylhexyl)aminomethyl]- 1 1
1 1 1 1 1- anticorrosive agent benzotriazole (F) Phosphate F-1
Aluminum phosphite 5 5 5 5 5 5 Anticorrosive Ca F-2 Amorphous
silicon dioxide, pigment exchanged calcium hydroxide 5 5 silica (G)
Phosphate ester G-1 2-methacryloyloxyethyl acid phosphate 3 3 3 3 3
3 3 (H) Lubricant H-1 Micronized polyethylene wax (I) Fluorescent
whitening I-1 2,5-thiophenediylbis(5-tert-butyl-1,3- 0.5 agent
benzoxazole) Total 100 100 100 100 100 100 100 100
[Testing Methods for Evaluation]
1. Evaluation of Corrosion Resistance (Salt Spray Test)
The corrosion resistance of the photocurable compositions obtained
in the examples and comparative examples was evaluated in the
following manner in accordance with the salt spray test described
in JIS Z2371.
First, each of the above-described photocurable compositions was
applied by spraying it atop a steel sheet so that the coating
thickness of the resulting photocured coating would be 20
micrometers.+-.1 micrometer, then it was irradiated with
ultraviolet light to cure the applied coating and obtain a steel
sheet with a photocured coating. As the steel sheet, a carbon steel
sheet (SPCC-SD, 150 mm.times.70 mm.times.0.8 mm) which had been
treated with a zinc phosphating solution (Paltec Test Panels Co.
Ltd.) so as to form a phosphate layer with a thickness of about 1
micrometer (hereinafter referred to as a zinc phosphated steel
sheet) was used. An air sprayer manufactured by Nordson K.K was
used as a spraying device. Curing with ultraviolet rays was carried
out by ultraviolet ray irradiation using an ultraviolet ray
irradiation apparatus manufactured by Eye Graphics Co., Ltd. under
the condition of 1000 mJ/cm.sup.2 (measured with an illuminometer
manufactured by TOPCON Corporation). The thickness of the
photocured coating which was formed was ascertained using an
electromagnetic film thickness meter manufactured by Kett Electric
Laboratory.
A salt spray test was carried out on the resulting steel sheet with
a photocured coating (Test Piece 1). The salt spray test was
carried out using a testing machine manufactured by Suga Test
Instruments Co., Ltd. Test Piece 1 was removed in order to examine
it for the presence or absence of rust after the passage of 100
hours, 200 hours, 500 hours, 750 hours, and 1000 hours. The
criterion for the occurrence of rust was that there was rust if
even one dot-shaped area of rust was observed. Test pieces which
did not have any rust after 750 hours (Score A or B in the
following criterion for evaluation) were considered acceptable.
Criterion for evaluation of corrosion resistance: A: No rust
observed after 1000 hours, B: No rust observed after 750 hours, C:
No rust observed after 500 hours, D: Occurrence of rust before 500
hours.
2. Evaluation of the Adhesion of the Photocured Coating to a
Substrate Before and after a Heat Cycle Test
The steel sheets used in this test were the above-described zinc
phosphated steel sheet and a stainless steel sheet having a Cr
content of 13 mass percent which had been finished by grinding (150
mm.times.70 mm.times.2 mm). The photocurable compositions obtained
in the examples and the comparative examples were applied by
spraying to the steel sheets, and then they were irradiated with
ultraviolet rays to cure the applied coating and obtain steel
sheets with a photocured coating. The conditions for application
and curing were the same as the conditions for to above-described
Test 1 (evaluation of corrosion resistance). Cross-shaped slits
with a length of 20 mm were made to a depth that reached the steel
substrate in the photocured coating using a cutting knife to create
a condition in which peeling could easily progress.
Using Test Piece 2 obtained in the above manner, (1) adhesion of
the photocured coating to a substrate before a heat cycle test, and
(2) adhesion of the photocured coating to a substrate after a heat
cycle test were evaluated.
(1) Before the heat cycle test: Adhesion was evaluated using a
typical tape peeling test based on JIS K5600. Only test pieces
having Score 1 or 0 (Score A or B in the following criterion for
evaluation) were evaluated as acceptable in accordance with the
evaluation standards set forth in JIS K5600.
Criterion for evaluation of adhesion before a heat cycle test A:
Score 0 in the tape peeling test based on JIS K5600, B: Score 1 in
the tape peeling test based on JIS K5600, C: Score 2 in the tape
peeling test based on JIS K5600, D: Score 3 or poorer in the tape
peeling test based on JIS K5600.
(2) After the heat cycle test: A heat cycle test was performed by
placing the above-described Test Piece 2 into a thermostat and
carrying out 20 cycles of holding it in an environment at
80.degree. C. and 30% relative humidity for 16 hours and then
holding it for 8 hours at a temperature of -45.degree. C. The
percent of peeled area of the photocured coating was measured after
the test. Only test pieces for which the percent of area peeled
from the slits was less than 5% (Score A or B in the following
criterion for evaluation) were considered acceptable.
Criterion for evaluation of adhesion after a heat cycle test A: No
peeling from the slits after the heat cycle test, B: Less than 5%
of area peeled from the slits after the heat cycle test, C: At
least 5% and less than 10% of area peeled from the slits after the
heat cycle test, D: At least 10% of area peeled from the slits
after the heat cycle test.
3. Method of Measuring Turbidity
The photocurable compositions obtained in the examples and
comparative examples were applied using a film applicator to a
biaxially oriented PET (polyethylene terephthalate) film so that
the film thickness after curing would be 25 micrometers. The
applied coatings were then irradiated with infrared rays to obtain
a photocured coating. The turbidity of the coated film having this
photocured coating was measured using a haze meter (NDH2000, Nippon
Denshoku Industries Co., Ltd., light source: halogen lamp rated at
5 V and 9 W (incident aperture diameter of 20 mm)).
4. Evaluation of Lubricating Properties (Coefficient of
Friction)
In order to evaluate the lubricating properties (coefficient of
friction) of the coating surface, a commercially available Bowden
friction tester (Shinko Engineering Co., Ltd.) was used. In the
Bowden friction tester, a steel ball was moved back and forth in a
straight line on a coating formed on a steel sheet while a load was
applied to the ball. The coefficient of friction was measured from
the frictional force and the pressing load at that time.
The specific procedure was as follows. First, a photocurable
composition obtained in the examples or comparative examples was
applied atop the zinc phosphated steel sheet with a bar coater so
that the coating thickness of the photocured coating would be 20
micrometers.+-.1 micrometer, then it was irradiated with
ultraviolet rays to cure the coating and obtain a steel sheet with
a photocured coating. The curing conditions were the same as the
conditions in above-described Test 1 (evaluation of corrosion
resistance). The resulting test pieces were cut to a size of 100
mm.times.20 mm and placed on the Bowden friction tester. A
commercially available steel ball made of SUJ2 steel with an outer
diameter of 3/16 inches (Amatsuji Steel Ball Manufacturing Co.,
Ltd.) which had been adequately degreased was used as the steel
ball in the Bowden friction test. The steel ball was moved back and
forth 30 times with a pressing load of 1 kgf, a sliding speed of 4
mm/sec, and a sliding width of 10 mm, and the average coefficient
of friction was determined. Lubricating properties were evaluated
using a coefficient of friction of 0.2 as a standard. It was
determined that a coefficient of friction of 0.2 or below indicated
good lubricating properties.
TABLE-US-00002 TABLE 2 Examples Comparative Examples Test Item Test
Piece 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 Corrosion resistance Zinc B
B B B A B A A A A C C C D D C phosphated steel sheet Adhesion
Before Zinc A A A A A A A A A A C C C B B D heat phosphated cycle
test steel sheet Stainless A A A A A A B A A A D D D C C D steel
sheet After heat Zinc A A A A A A B A A A C C C B B D cycle test
phosphated steel sheet Stainless A A A A A A B A A A D D D C C D
steel sheet Turbidity (%) -- 10 10 10 10 14 10 25 35 25 10 10 10 10
10 1 10 Lubricating properties Zinc 0.13 0.14 0.14 0.13 0.08 0.14
0.16 0.17 0.13 0.12 0.29 0.- 31 0.33 0.5 0.3 0.26 (Friction
coeefficient) phosphated steel sheet Corrosion resistance: A = No
rust after 1000 hr, B = No rust after 750 hr, C = No rust after 500
hr, D = Rust observed before 500 hr. Adhesion before heat cycle
test (Score of tape peeling, JIS K5600): O = A, 1 = B, 2 = C, 3 or
more = D Adhesion after heat cycle test (% peeled area from slits):
0% = A, less than 5% = B, from 5% to less than 10% = C, 10% or more
= D
As shown in Table 2, in each of Examples 1-10, there was no
formation of rust after 750 or more hours in the salt spray test,
and it was determined that corrosion resistance was acceptable. The
adhesion to substrates evaluated in the tape peeling test was 0 or
1 by the evaluation standard of JIS, so the adhesion to a substrate
before the heat cycle test was evaluated as acceptable. The
adhesion to a substrate after the heat cycle test was a peeling
area percentage from slits of less than 5%, so the adhesion to the
substrate after the heat cycle test was evaluated as acceptable. In
each of Examples 1-8, the coefficient of friction using a Bowden
friction tester was at most 0.2, so the lubricating properties were
evaluated as acceptable.
In contrast, in all of Comparative Examples 1-6, rust developed by
500 hours or 750 hours in the salt spray test, so corrosion
resistance was evaluated as unacceptable. The adhesion to the
substrate evaluated by the tape peeling test and the adhesion to
the substrate after the heat cycle test was unacceptable except for
Comparative Examples 4 and 5 in which the substrate was a zinc
phosphated steel sheet. In particular, the adhesion to a stainless
steel sheet was extremely poor. In each of Comparative Examples
1-6, the coefficient of friction in the Bowden friction test was at
least 0.2, so the lubricating properties were evaluated as
poor.
5. Actual Performance Test
(5-1) In order to confirm the performance of a photocured coating
according to the present invention on an actual threaded joint for
steel pipes, coating treatment was carried out in the following
manner using the photocurable compositions obtained in Examples 5
and 10 on the surface including the male threads of a threaded
joint which was formed on the outer surface at the end of a carbon
steel pipe for use as an oil country tubular good (VAMTOP.TM.)
having an outer diameter of 133/8 inch.
After a zinc phosphate coating was formed with a thickness of 8
micrometers (using a zinc phosphating solution from Nihon
Parkerizing Co., Ltd.: Palbond 181X) on the outer surface including
the male threads (pin surface) at the end of the steel pipe, the
photocurable composition was applied by spraying while rotating the
steel pipe on turning rollers and moving a spray nozzle in the
axial direction. Irradiation with ultraviolet rays was then carried
out while rotating the steel pipe to cure the applied coating. A
small steel sheet was attached to the steel pipe at a location near
the threaded portion, the threaded portion and the steel sheet were
simultaneously coated, and the coating conditions were adjusted so
that the thickness of the photocured coating on the steel sheet was
25 micrometers. The curing conditions were the same as the
conditions when forming the test piece of above-described Test 1
(evaluation of corrosion resistance), and the cumulative
irradiation was 1000 mJ/cm.sup.2. The other conditions were as
indicated in 5-2 described below.
A steel pipe having a photocured coating obtained in this manner
was left outdoors for at least 3 months near the seashore in an
equatorial region having a high temperature and high humidity, and
it was left for at least 3 months in winter outdoors near the
seashore in northern Europe where the winter is extremely cold. In
both cases, it was confirmed that there was no rust or peeling of
the coating.
(5-2) A makeup and breakout test of a threaded joint for oil
country tubular goods was also carried out. A photocured coating
was formed on a surface including the male threads on the pin of a
threaded joint formed on the outer surface at the end of a steel
pipe, and a solid lubricating coating was formed on a surface
including the female threads of the mating box (formed on the inner
surface of a coupling). As steel pipes for oil country tubular
goods, steel pipes made of carbon steel or 13 Cr steel having a
diameter of 31/2 inches, 7 inches, 95/8 inches, or 133/8 inches
were used. The thread shape was VAMTOP (trademark).
In the case of the carbon steel, coating treatment was carried out
in the following manner on the surfaces of a pin and a box.
The surface including the male threads of a pin was first treated
by immersion in a zinc phosphating solution (the same as used in
test 5-1 described above) at 75-85.degree. C. to form a zinc
phosphate coating with a thickness of 8 micrometers. Then a coating
composition comprising the photocurable composition obtained in
Example 5 or 10 was applied by spraying atop the zinc phosphate
coating in the same manner as described in 5-1, and the coating
composition was irradiated with ultraviolet rays to cure the
applied coating and form a cured coating with a thickness of 25
micrometers. The curing conditions were cumulative irradiation of
1000 mJ/cm.sup.2, UV lamp: air-cooled mercury lamp, UV lamp output:
4 kW, wavelength of ultraviolet rays: 260 nm.
The surface including the female threads of a box was first treated
by Ni strike plating and then by Cu--Sn--Zn alloy plating, both
done by electroplating, to form a plated coating with a total
thickness of 8 micrometers. A composition for forming a solid
lubricating coating having the below-described composition was
heated at 120.degree. C. to obtain a molten state, and then the
molten composition was applied by spraying atop the plated coating
on the box which was preheated to 120.degree. C. to form a solid
lubricating coating with a thickness of 50 micrometers.
The composition of the solid lubricating coating-forming
composition (on mass % basis) was as follows.
9% of polyethylene homopolymer (LICOWAX.TM. PE 520 of CLARIANT)
15% of carnauba wax
15% of zinc stearate
5% of liquid polyalkyl methacrylate (IVSCOPLEX.TM. 6-950 of
ROHMAX)
40% of corrosion suppressant (NA-SUL.TM. Ca/W1935 of King
Industries, Inc.)
3.5% of graphite fluoride
1% of zinc oxide
5% of titanium dioxide
5% of bismuth trioxide
1% of silicone (polydimethyl siloxane), and
0.3% of IRGANOX.TM. and 0.2% of IRGAFOS.TM. as antioxidants (both
of Ciba-Geigy).
In the case of the 13 Cr steel, a photocured coating was formed on
the surface including the male threads of the pin without forming a
zinc phosphate coating. The conditions were otherwise the same as
for the carbon steel.
Makeup and breakout were repeated 10 times using a threaded joint
having a pin and a box which had undergone the above-described
surface treatment. During the initial stage of makeup, it was
ascertained that there was no damage to the threaded portions due
to cross threading. In addition, it was confirmed that galling did
not develop and lubricating properties did not worsen during 10
cycles of makeup and breakout.
* * * * *